Python学习笔记之json.dump和json.load

10-11 喜欢的数字：编写一个程序，提示用户输入他喜欢的数字，并使用json.dump()将这个数字存储到文件中。再编写一个程序，从文件中读取这个值，并打印消息“I know your favorite number! It’s _____.”。

favorite_number.py

 import json

 def favorite_number():
     """提示用户输入喜欢的数字"""
     filename = 'favorite_number.json'
     number = input("请输入你喜欢的数字：")
     with open(filename, 'w') as f_obj:
         json.dump(number, f_obj)

 favorite_number()

get_favorite_number.py

 import json

 def get_favorite_number():
     """获取文件内容"""
     filename = 'favorite_number.json'
     with open(filename) as f_obj:
         get_number = json.load(f_obj)

     print("I know your favorite number! It’s " + str(get_number) + ".")

 get_favorite_number()

10-12 记住喜欢的数字：将练习10-11 中的两个程序合而为一。如果存储了用户喜欢的数字，就向用户显示它，否则提示用户输入他喜欢的数字并将其存储到文件中。运行这个程序两次，看看它是否像预期的那样工作。

 import json

 def get_stored_number():
     filename = 'favorite_number.json'
     try:
         with open(filename) as f_obj:
             number = json.load(f_obj)
     except FileNotFoundError:
         return None
     else:
         return number

 def favorite_number():
     """提示用户输入喜欢的数字"""
     filename = 'favorite_number.json'
     number = input("请输入你喜欢的数字：")
     with open(filename, 'w') as f_obj:
         json.dump(number, f_obj)
     return number

 def get_favorite_number():
     """获取文件内容"""
     # filename = 'favorite_number.json'
     # with open(filename) as f_obj:
     #     get_number = json.load(f_obj)
     number = get_stored_number()
     if number:
         print("I know your favorite number! It’s " + str(number) + ".")
     else:
         number = favorite_number()
         print("I know your favorite number! It’s " + str(number) + ".")

 get_favorite_number()

10-13 验证用户：最后一个remember_me.py 版本假设用户要么已输入其用户名，要么是首次运行该程序。我们应修改这个程序，以应对这样的情形：当前和最后一次运行该程序的用户并非同一个人。

为此，在greet_user()中打印欢迎用户回来的消息前，先询问他用户名是否是对的。如果不对，就调用get_new_username()让用户输入正确的用户名。

原remember_me.py代码

 import json

 def get_stored_username():
     """如果存储了用户名，就获取它"""
     filename = 'username.json'
     try:
         with open(filename) as f_obj:
             username = json.load(f_obj)
     except FileNotFoundError:
         return None
     else:
         return username

 def get_new_username():
     """提示用户输入用户名"""
     username = input("What is your name? ")
     filename = 'username.json'
     with open(filename, 'w') as f_obj:
         json.dump(username, f_obj)
     return username

 def greet_user():
     """问候用户，并指出其名字"""
     username = get_stored_username()
     if username:
         print("Welcome come back, " + username + "!")
     else:
         username = get_new_username()
         print("We will remember you when you come back, " + username + "!")

 greet_user()

修改之后remember_me.py代码

 import json

 def get_stored_username():
     """如果存储了用户名，就获取它"""
     filename = 'username.json'
     try:
         with open(filename) as f_obj:
             username = json.load(f_obj)
     except FileNotFoundError:
         return None
     else:
         return username

 def get_new_username():
     """提示用户输入用户名"""
     username = input("What is your name? ")
     filename = 'username.json'
     with open(filename, 'w') as f_obj:
         json.dump(username, f_obj)
     return username

 def greet_user():
     """问候用户，并指出其名字"""
     username = get_stored_username()
     if username:
         msg = "Are you " + username + "? (y/n) "
         correct = input(msg)
         if correct == 'y':
             print("Welcome come back, " + username + "!")
         else:
             username = get_new_username()
             print("We will remember you when you come back, " + username + "!")

     else:
         username = get_new_username()
         print("We will remember you when you come back, " + username + "!")

 greet_user()